**2. Nanomaterials in plant growth**

The increase requirement of global food production is related nowadays with the necessity of application new technology for enhancing crop yield in order to satisfy the global food security. As a modern trend in this view, the application of nanotechnology solutions can bring a response to grave problem of different deficiencies in human population as deficiencies of iron, zinc, selenium, calcium, phosphorus or vitamin A. The nanotechnology can offer solutions as micronutrients in agriculture in order to optimize the deficient presence of these substances in soil, by their use in fertilization. Besides the possible studied benefits, it is stated [1] that the nanomaterials use in agriculture may pose unforeseeable risks due to the intentional input of nanomaterials in the environment that can led to human exposure related to bioaccumulation in crops and soil and as a consequence in the food chain.

The great challenge of modern agriculture related to the use of nanotechnology is to regulate the products with the nano content in the condition where the nanomaterials pose problems to the regulatory bodies and on the other hand there is a lack of knowledge to the possible effect on the plant growth, i.e. to the genetics of plants. The possible use of nanomaterials in agriculture is a new nanotechnology solution under development now for a dozen years [4, 5] as studies regarding the use of nanoscale nutrients (metals, metal oxides, carbon) to suppress crop diseases [6]. In this view, the problem of agriculture in managing the crop disease is related to different attempts as genetic breeding, new pesticides products or new eradication protocols with the effect of the development of host plant resistance. Genetically modified plants raises different ethical problems related to the effect to the metabolism of human body, and this is a serious public concern.

A possible alternative for suppressing crop disease is the managing of plant nutrition statue and in this perspective the major limitation is that different crops have different nutrients requirements and the nutrient interacts with the level of plant disease in variable ways. As an example, the micronutrients are critical in the defense against crop disease where tissue infection induced reactions that conduced to the production of inhibitory secondary metabolites. These metabolites are generally generated by enzymes that requires activation by micronutrients cofactors, e.g. Mn, Cu and Zn as activating host defense enzymes i.e. phenylalanine or ammonia

lyase. The availability of micronutrients level is related to soil characteristics, e.g. Fe, Mn, Zn are deficient in alkaline soils which limit uptake by roots and by consequence exposed roots to infections. Another way for enhancing disease defense is connected to non-essential elements, e.g. Al or Si, that offers resistance to a number of foliar and root pathogens although their presence in soil (e.g. Si) is frequently limited. As regarding Al, its application has been limited due to the fact that the over-application can cause significant crop damage and yield reduction, and insufficient presence modifies the acidity of soil [7]. The important characteristics of the nanoscale metals and metal oxides is the greatly their availability and translocation within plants. In the process of producing nanomaterials to be applied in agriculture there are used besides chemical and physical methods for synthesis the biosynthesis using plant extracts. The traditional method is the synthesis on chemical route, namely the reduction in liquid phase with common reducing agents as; citric acid, hydroxylamine, cellulose, hydrogen peroxide, sodium carbonate and sodium hydroxide. In the solutions are added stabilizing agents in order to assure uniform particle distribution and dispersion, agents such as: polyvinyl alcohol and sodium polyacrylate. The physical methods for synthesis include laser ablation, chemical vapor deposition (CVD), sonochemical reduction, supercritical fluids or gamma radiation. In the case of carbon, the fullerene synthesis is realized in arc discharge or gas combustion and carbon nanotubes are produced by CVD in the decomposition process of gaseous hydrocarbons. Different nano products that can be used as fertilizers have been patented in the last years as: active nano-grade organic fine humic (CN 1472176-A, Wu et al.); oxide nano rare earth (CN1686957-A, Wang et al.), carbon nanomaterials (US 0174032-A1, Lui et al.); nanosilver (KR 000265-A, Kim et al.); nano diatomite and zeolite (US 0115469-A1, Yu et al.), nano-selenium (US 0326153-A1, Yin et al.) or nano-silicon carrier (US 0225412-A1, Sardari et al.). The high-surface area nanoscale materials conduced to a more efficient retain of nutrients and represents a stable reservoir to plants [8], raising the potential for enhanced plants growth. The use of traditional is characterized by fertilizers with active ingredients that have low water solubility, the result being an inefficient availability to plants and furthermore a lack of control to pathogen agents. The nanofertilizers offer controlled release and synchronization of the nutrient flux over time with the uptake, minimizing the wasteful interactions with soil or air that conduced to nutrients loss. From the roots of the plants the nanomaterials as ZnO, TiO2, CeO2, Fe3O4, Ni(OH)2, C70 fullerenes, Al, Cu, Ag, carbon nanotubes (CNT), are uptake and translocated to plant stem where partly are deposited (C70, Fe3O4,CeO2, Ni(OH)2) or partly are foliar deposited (Al, Ag, Cu, Zn, ZnO, CeO2, Fe3O4, C70). The root cell of a plant has different absorption zones for different kinds of nanomaterials, for instance Fe3O4 has absorption areas in epidermis, cortex and cambium; Ni(OH)2 in epidermis, cortex, cambium and metaxylem, Ag in epidermis and cortex or Ag2+ in epidermis, cortex, endodermis, and metaxylem.

Regarding nanomaterials exposure there exists a positive experience impact on crop growth and pathogen inhibitions, as related to antimicrobial activity for Ag, ZnO, Mg, Si or TiO2. The effect on different plants of the foliar exposure to nanomaterials as ZnO conduced to increase in shoot length (15.1%), root length (4.2%) [9], increase in chlorophyll (24.4%) soluble leaf protein (38.7%) or increase in acid phosphatase (76.9%), alkaline phosphatase (61.7%) and phytase (>3x). The effect of tobacco culture cell exposure to MWCNT (multiple wall carbon nano tubes) conduced to enhanced cell growth and regulate cell division by activating water channel protein [10] and the effect of 50 μg/ml on tomato roots to MWCNT conduced to enhanced fresh and dry mass besides changes in gene expression (water channel protein) [11]. The foliar and root application of nanoparticles of Fe2O3 conduced to the increasing of root elongation and to the increase of photosynthetic

**55**

*Application of Nanotechnology Solutions in Plants Fertilization*

parameters by foliar application [12]. The application of Mn in concentration 0.05–1 mg/L on Mung bean roots in a Hoagland culture solution conduced to an increase in shoot and root length, dry and fresh biomass and rootlet number [13]. The effect of spinach roots exposure to TiO2 nanoparticles present in soil conduced to an enhanced growth rate and chlorophyll as well as an enhanced rubisco activity and photosynthetic rate [14]. The silver nanoparticles exhibit an intense inhibitory activity to microorganisms, in this regard Ag NPs damaged and penetrate the cell membrane subsequently reducing the infection [15]. Another nanomaterial with intense antimicrobial activity is ZnO NPs that is effective to pathogen control growth, also characterized by a lower toxicity in comparison to Ag and with benefits on soil fertility. The application of ZnO NPs conduced to systemic disruption of cellular function of pathogens as *Botrytis cinerea* or *Penicillium expansum* resulting in hyphal malformation and fungal depth [16]. Another promising amendment is TiO2 NPs due to their combined photo-catalytic and antimicrobial activity, e.g. application of TiO2 NPs reduced *P. cubensis* infection of cucumber by 91% and increase photosynthetic activity by 30% [17]. One of the most popular cultures is that of wheat, in this case the foliar application of Ti NPs at 20 g/l it increased stem elongation, biomass, flowering, ear mass and seed number [18]. Nanomaterials fertilizing activity is influenced by the chemical and physical characteristics of the environment soil, air and water. The initial properties of NM can suffer different transformations due to the interactions with both biotic and abiotic soil components and these modifications can influence the stability of NPs, transport and aggregation and availability to plants. Necessary micronutrients as Cu, Fe, Mn or Zn become less availability from the soil when pH is approaching to the limit of 7.0 and subsequently there exist a lower uptake to plants roots and compromising the nutritional status [19]. It is reported [20] a pH-dependence of humic acid adsorption onto nanoparticles of TiO2, Al2O3 and ZnO where the electrostatic interactions and ligand exchange with SiO2 is responsible for selective adsorption onto oxide surface. Due to different limitations related to soil characteristics and their content in macro and micro nutrients, it became important the foliar applications of fertilizers, in particular the nanomaterial nutrients. The entrance gate for micronutrients is the leaves through stomata and cuticle structures as the studies in literature have presented [21]. In case of watermelon [22] the pathway leaf-to-root translocation of nanomaterials after a foliar application presented an important content of Ti, Mg or Zn nanoparticles that exist in root tissue a fact that shows the effective action of foliar application of nanomaterials. The possible route of biosynthesis of nanoparticles, e.g. ZnO by extracellular secretions of *Aspergillus fumigatus* TFR-8 and their applications as a foliar spray conduced in case of bean plants [23] to an increase of physiological parameters i.e. biomass, shoot/root length, root area or chlorophyll content and on the other hand the residual protein from fungal extract increased nanoparticle stability. Regarding TiO2 nanomaterials is stated [24] that the application on different crops, e.g. wheat or soybean has increased the yield and reduced the pathogenic diseases, these effects being based on surface properties of TiO2 nanoparticles as their photo-catalytic characteristics. Another nanomaterial applied to cucumber leaves is CeO2 [25] in nano-powder form, showed a high leaf-to-root translocation suggesting a phloem-based transport throughout the plant. Foliar applied nanoscale amendments dedicated to pathogen control are related to antifungal activity of CuO2 nanomaterial or Ag nanoparticles. Tested on tomato infected with *Phytothphora infestans* the effect of CuO2 nanomaterial [26] showed an increased protection (73.5%) as compared to bulk amendment (57.8%) promoting the use of nanoscale amendments both to suppress disease and enhanced the nutrient action of nanomaterials. The antifungal activity of Ag nanoparticles is based on the accumulation in the fungal hyphae that disrupted cellular function, an

*DOI: http://dx.doi.org/10.5772/intechopen.91240*

### *Application of Nanotechnology Solutions in Plants Fertilization DOI: http://dx.doi.org/10.5772/intechopen.91240*

*Urban Horticulture - Necessity of the Future*

lyase. The availability of micronutrients level is related to soil characteristics, e.g. Fe, Mn, Zn are deficient in alkaline soils which limit uptake by roots and by consequence exposed roots to infections. Another way for enhancing disease defense is connected to non-essential elements, e.g. Al or Si, that offers resistance to a number of foliar and root pathogens although their presence in soil (e.g. Si) is frequently limited. As regarding Al, its application has been limited due to the fact that the over-application can cause significant crop damage and yield reduction, and insufficient presence modifies the acidity of soil [7]. The important characteristics of the nanoscale metals and metal oxides is the greatly their availability and translocation within plants. In the process of producing nanomaterials to be applied in agriculture there are used besides chemical and physical methods for synthesis the biosynthesis using plant extracts. The traditional method is the synthesis on chemical route, namely the reduction in liquid phase with common reducing agents as; citric acid, hydroxylamine, cellulose, hydrogen peroxide, sodium carbonate and sodium hydroxide. In the solutions are added stabilizing agents in order to assure uniform particle distribution and dispersion, agents such as: polyvinyl alcohol and sodium polyacrylate. The physical methods for synthesis include laser ablation, chemical vapor deposition (CVD), sonochemical reduction, supercritical fluids or gamma radiation. In the case of carbon, the fullerene synthesis is realized in arc discharge or gas combustion and carbon nanotubes are produced by CVD in the decomposition process of gaseous hydrocarbons. Different nano products that can be used as fertilizers have been patented in the last years as: active nano-grade organic fine humic (CN 1472176-A, Wu et al.); oxide nano rare earth (CN1686957-A, Wang et al.), carbon nanomaterials (US 0174032-A1, Lui et al.); nanosilver (KR 000265-A, Kim et al.); nano diatomite and zeolite (US 0115469-A1, Yu et al.), nano-selenium (US 0326153-A1, Yin et al.) or nano-silicon carrier (US 0225412-A1, Sardari et al.). The high-surface area nanoscale materials conduced to a more efficient retain of nutrients and represents a stable reservoir to plants [8], raising the potential for enhanced plants growth. The use of traditional is characterized by fertilizers with active ingredients that have low water solubility, the result being an inefficient availability to plants and furthermore a lack of control to pathogen agents. The nanofertilizers offer controlled release and synchronization of the nutrient flux over time with the uptake, minimizing the wasteful interactions with soil or air that conduced to nutrients loss. From the roots of the plants the nanomaterials as ZnO, TiO2, CeO2, Fe3O4, Ni(OH)2, C70 fullerenes, Al, Cu, Ag, carbon nanotubes (CNT), are uptake and translocated to plant stem where partly are deposited (C70, Fe3O4,CeO2, Ni(OH)2) or partly are foliar deposited (Al, Ag, Cu, Zn, ZnO, CeO2, Fe3O4, C70). The root cell of a plant has different absorption zones for different kinds of nanomaterials, for instance Fe3O4 has absorption areas in epidermis, cortex and cambium; Ni(OH)2 in epidermis, cortex, cambium and metaxylem, Ag in epidermis

and cortex or Ag2+ in epidermis, cortex, endodermis, and metaxylem.

Regarding nanomaterials exposure there exists a positive experience impact on crop growth and pathogen inhibitions, as related to antimicrobial activity for Ag, ZnO, Mg, Si or TiO2. The effect on different plants of the foliar exposure to nanomaterials as ZnO conduced to increase in shoot length (15.1%), root length (4.2%) [9], increase in chlorophyll (24.4%) soluble leaf protein (38.7%) or increase in acid phosphatase (76.9%), alkaline phosphatase (61.7%) and phytase (>3x). The effect of tobacco culture cell exposure to MWCNT (multiple wall carbon nano tubes) conduced to enhanced cell growth and regulate cell division by activating water channel protein [10] and the effect of 50 μg/ml on tomato roots to MWCNT conduced to enhanced fresh and dry mass besides changes in gene expression (water channel protein) [11]. The foliar and root application of nanoparticles of Fe2O3 conduced to the increasing of root elongation and to the increase of photosynthetic

**54**

parameters by foliar application [12]. The application of Mn in concentration 0.05–1 mg/L on Mung bean roots in a Hoagland culture solution conduced to an increase in shoot and root length, dry and fresh biomass and rootlet number [13]. The effect of spinach roots exposure to TiO2 nanoparticles present in soil conduced to an enhanced growth rate and chlorophyll as well as an enhanced rubisco activity and photosynthetic rate [14]. The silver nanoparticles exhibit an intense inhibitory activity to microorganisms, in this regard Ag NPs damaged and penetrate the cell membrane subsequently reducing the infection [15]. Another nanomaterial with intense antimicrobial activity is ZnO NPs that is effective to pathogen control growth, also characterized by a lower toxicity in comparison to Ag and with benefits on soil fertility. The application of ZnO NPs conduced to systemic disruption of cellular function of pathogens as *Botrytis cinerea* or *Penicillium expansum* resulting in hyphal malformation and fungal depth [16]. Another promising amendment is TiO2 NPs due to their combined photo-catalytic and antimicrobial activity, e.g. application of TiO2 NPs reduced *P. cubensis* infection of cucumber by 91% and increase photosynthetic activity by 30% [17]. One of the most popular cultures is that of wheat, in this case the foliar application of Ti NPs at 20 g/l it increased stem elongation, biomass, flowering, ear mass and seed number [18]. Nanomaterials fertilizing activity is influenced by the chemical and physical characteristics of the environment soil, air and water. The initial properties of NM can suffer different transformations due to the interactions with both biotic and abiotic soil components and these modifications can influence the stability of NPs, transport and aggregation and availability to plants. Necessary micronutrients as Cu, Fe, Mn or Zn become less availability from the soil when pH is approaching to the limit of 7.0 and subsequently there exist a lower uptake to plants roots and compromising the nutritional status [19]. It is reported [20] a pH-dependence of humic acid adsorption onto nanoparticles of TiO2, Al2O3 and ZnO where the electrostatic interactions and ligand exchange with SiO2 is responsible for selective adsorption onto oxide surface. Due to different limitations related to soil characteristics and their content in macro and micro nutrients, it became important the foliar applications of fertilizers, in particular the nanomaterial nutrients. The entrance gate for micronutrients is the leaves through stomata and cuticle structures as the studies in literature have presented [21]. In case of watermelon [22] the pathway leaf-to-root translocation of nanomaterials after a foliar application presented an important content of Ti, Mg or Zn nanoparticles that exist in root tissue a fact that shows the effective action of foliar application of nanomaterials. The possible route of biosynthesis of nanoparticles, e.g. ZnO by extracellular secretions of *Aspergillus fumigatus* TFR-8 and their applications as a foliar spray conduced in case of bean plants [23] to an increase of physiological parameters i.e. biomass, shoot/root length, root area or chlorophyll content and on the other hand the residual protein from fungal extract increased nanoparticle stability. Regarding TiO2 nanomaterials is stated [24] that the application on different crops, e.g. wheat or soybean has increased the yield and reduced the pathogenic diseases, these effects being based on surface properties of TiO2 nanoparticles as their photo-catalytic characteristics. Another nanomaterial applied to cucumber leaves is CeO2 [25] in nano-powder form, showed a high leaf-to-root translocation suggesting a phloem-based transport throughout the plant. Foliar applied nanoscale amendments dedicated to pathogen control are related to antifungal activity of CuO2 nanomaterial or Ag nanoparticles. Tested on tomato infected with *Phytothphora infestans* the effect of CuO2 nanomaterial [26] showed an increased protection (73.5%) as compared to bulk amendment (57.8%) promoting the use of nanoscale amendments both to suppress disease and enhanced the nutrient action of nanomaterials. The antifungal activity of Ag nanoparticles is based on the accumulation in the fungal hyphae that disrupted cellular function, an

intense process related to a higher ion release on the increased nanoparticle surface area [27]. It is worth to mention that the problem of *in planta* translocation, i.e. the way that the foliar application of nanoscale nutrients affects root pathogens, is still under research in the sense that pathogens can be released after shoot-root transfer or the induced host resistance. A non-classical nutrient besides metal and metaloxides there is based on carbon nanomaterials in the forms of C60/70 fullerenes, carbon nanoparticles, or single/multiple wall carbon nanotubes (SWCNT/MWCNT). An extended study [11] in literature upon the action of MWCNT, SWCNT, graphene and bulk activated carbon onto tomato plants grown in artificial medium revealed an enhancement of biomass by stimulating the growth. The molecular analysis upon the action of MWCNT has shown a stimulation of cell division and plant growth due to the activation of water channels (aquaporins) and regulatory genes for cell division and extension. Carbon nanomaterials exposure can alter the different co-existing organic contaminants in various kinds of soils. In this regards, carbon nanomaterials presents toxicity to soil microorganisms, with accent to SWCNT including fungal community. Carbon nanomaterials have potential to enhance plant growth, nutrient uptake, seed germination or fruit yield the most promising one being MWCNT with positive effects on different crop species. The large inters in the use of nanomaterials is based on the increase global production of nanomaterials and their possible application in agriculture with hazards and risks to be investigated. An exposed [28, 29] "realistic exposure scenario" for TiO2, Ag and carbon nanotubes proposed the doses of 0.4, 0.02 and 0.01 μg/kg/year although the relationship between these values and the actual concentration in the environment is not known.

It is worth to mention, that in general the discussion to nanomaterials in agriculture refers also to a most prominent fraction of nanomaterials that are non-solids comprising nanoscale structures that can encapsulate an active ingredient in plan protection product. Generally active substances have poor solubility in water and at room temperature are brought to solution with organic (co)solvents. In order to avoid the use of organic (co)solvents one solution is stated [30] the use of oil/water emulsions. Generally the physical appearance of non-solid nanomaterials are lipid base in liposomes, micelles or cochleates, in polymer based in micelles, nanosphere, nanocapsules and polymersomes or in emulsions base as liquid crystals and microemulsions. The nanomaterials in non-solid forms enhance the solubility and the coverage of the hydrophobic leaf surface together with the penetration of the active substances through the cuticula.

As presented, the characteristics of solid and non-solid nanomaterials have been investigated in the last decade in order to understand the effect of nanonutrients in culture fertilization as well as in plant protection with promising results together with various studies regarding the toxicity of nanoparticles in the environment.
